Accidental needle sticks from used and thereby contaminated needles expose both hospital personnel and other persons that come in contact with people that self-medicate to the risk of infection from blood-borne diseases.
Even though the majority of injection devices used is the normal syringe the use of pen needle injectors is becoming more and more popular since they provide the possibility of an easy and convenient self-administration of drugs. The pen-type injectors are also becoming the only choice for certain types of drugs because they are not delivered in ordinary single use syringes.
In order to reduce the risk of accidental needle sticks, many pen injectors have been arranged with needle shields that are capable of covering said needle after injection. These needle shields may be useful but they add to the complexity and number of components of the injector. Further, if the injector is designed to deliver multiple doses, then the needle has to be replaced after each injection. This adds to the risk of accidental needle sticks and if the injector is arranged with a needle cover, this will be in the way when the needle is to be replaced.
Injections where a liquid is expelled into the human body are usually performed either as intramuscular injections i.e. injections into the muscle tissue, or as subcutaneously injections i.e. injections into the subcutaneous tissue lying between the cutis and the muscle tissue. When performing intramuscular injections, long injections needles are used. The outside diameters of injection needles are indicated by a “G” and a gauge number increases with thinner needles. Thus the outside diameter of a G 23 is 0.60 mm and of a G 25 0.50 mm. Long injection needle has a diameter of 23 G for a 25 mm long injection needle and 25 G for a 16 mm long injection needle. It has for some years been known to provide long injection needles with safety protective devices in order to prevent accidental needle stick injuries. Such safety protective devices are e.g. known from EP 409 180 and U.S. Pat. No. 4,813,940. These known safety protective devices comprises a number of telescopic sleeves, which telescopic sleeves slides into each other in order to expose an injection needle covered by the telescopic sleeves when not in use. However, some medicines have to be injected subcutaneously i.e. in the subcutis lying between the cutis and a muscle membrane which cover the underlying muscles. When performing subcutaneous injections, short and thin injections needles are used and these short needles have also safety protective devices, wherein the combination of the short needle and the safety protective device is known as a safety pen needle.
A few safety pen needle solutions have been developed in order to minimize the risk of accidental needle sticks.
One such solution is disclosed in the U.S. Pat. No. 7,462,168. Therein is described a safety pen needle with a passive safety shield system. It comprises a central hub to which an injection needle is attached, where the needle is provided with an injection end and a non-injection end, and where the latter is intended to penetrate a septum of a medicament container when mounted. Outside the hub a sleeve is slidably arranged and further a shield is slidably arranged to the sleeve in a kind of telescopic manner. The sleeve and the shield are both urged in the proximal direction by a compression spring. When the injection is performed the shield is pushed into the sleeve, which in turn slides in relation to the hub, thereby exposing the injection end of the needle. When the shield is fully depressed in relation to the sleeve, it becomes locked to the sleeve and they move in tandem during continued penetration. When the device is removed after injection, the sleeve and shield are moved in the proximal direction by the compression spring until tabs on the sleeve enter lock out recesses on the hub such that the sleeve and thus the shield are locked and the needle is protected. Further the safety pen needle according to U.S. Pat. No. 7,462,168 comprises a safety system for the non-injection end of the needle. It comprises a non-injection end shield slidable in relation to the hub. A protrusion on the hub cooperates with tracks on the shield to first allow the shield to be pushed into the hub when mounted on a medicament container and then to lock said shield in an extended position when removed from the container, where the tracks have a first straight part and a latter inclined part with a depression for locking the shield. However, probably functioning correctly in covering the needle, the safety pen needle according to '168 comprises a lot of interacting components in order to obtain the desired function, which makes the design rather difficult to manufacture and thereby rather costly.
Another solution is found in EP1289587B1 which discloses a disposable double pointed safety pen needle having a needle hub to which a thin needle cannula is permanently fastened and which needle hub can be mounted onto a syringe comprising a dose setting and injection mechanism and a cartridge containing a liquid medicine to be injected subcutaneously into a human body. The needle hub is provided with a safety shield guided on the outside surface of the needle hub. The safety shield is urged in a direction away from the needle hub by a spring located between the needle hub and the safety shield. The safety shield has a number of protrusions guided in guiding tracks on the outside surface of the needle hub. The guiding tracks are designed such that the safety shield during injection is displaced towards the needle hub by a translation movement and after injection is longitudinally moved away from the needle hub by the spring and locked in an irreversible position where the safety shield covers the needle cannula and prevents accidental needle stick injuries. Since the shield is in contact with an injection site and the shield is moved by a translation movement, i.e. a rotationally longitudinal displacement, the contact between the shield and the injection site i.e. the skin of a patient, is affected by a friction which may result in an ineffective function of the safety pen needle.
A further solution is known from US 2005 065 476 A1 which discloses a safety needle assembly comprising a cylindrical housing adapted to be attached to a medical injection device, a needle cannula attached to the housing, a shield telescopically movable relatively to the housing for movement between a distal position where the shield covers the distal end of the needle cannula and a proximal position where at least a part of the distal end of the needle cannula is exposed, a spring located inside said housing urging the shield in the distal direction, and a locking element longitudinal having locking protrusions and being moved simultaneously with the shield relatively to the housing during use. However, US 2005 065 476 A1 also discloses that since the locking element is provided as a separate element located between the spring and the shield and moved simultaneously with the shield, the locking protrusion can be guided during the longitudinal movement of the locking element thereby eliminating the need for tracks or cams.